A bone-conduction type earphone is known that causes a vibration device contacting the ear to vibrate due to an audio signal, and that transmits such vibration to the cochlear duct (also called the “scala media”) in the inner ear via bone to thus allow auditory nerves floating in the lymph fluid to sense sound recorded in the audio signal.
The bone-conduction type earphone transmits sound without sealing air in the ear canal, and even while listening to music, a listener can thus recognize ambient sounds such as human voices. However, the sound transmitted to the cochlear duct is transmitted to the eardrums of both ears, and thus localization of sound (lateral separation) is insufficient.
In this context, Patent Literature 1 discloses an earphone that transmits sound to the ear canal cartilage. However, the structure of the disclosed earphone does not allow the vibration of the vibration device to be sufficiently transmitted to the ear canal cartilage. That is to say, a majority of the energy of vibration is transmitted to the ambient air. This transmission generates so-called “sound leakage” so that people in the vicinity are inconvenienced during use of the earphone. Further, sound is transmitted by vibration of an object that has mass rather than by compression waves in air, and thus high frequency vibration is difficult, and sound characteristics at high frequencies deteriorate.